Waste heat recovery system having a working fluid circuit

ABSTRACT

The invention relates to a waste heat recovery system having a working fluid circuit (1) for an internal combustion engine, comprising a first heat exchanger (2a) connected in an exhaust gas line (3) of the internal combustion engine (5) and a second heat exchanger (2b) inserted into a line, which are part of the working fluid circuit (1), which has at least an expansion machine (11), a condenser (12), and a fluid pump. According to the invention, a waste heat recovery system that is improved in particular in respect of an efficiency of the system is provided. This is achieved in that each of the two heat exchangers (2a, 2b) is assigned a fluid pump (15a, 15b). Said fluid pumps (15a, 15b) are combined in a two-stroke vane cell pump (16).

BACKGROUND OF THE INVENTION

The present invention relates to a waste heat recovery system having a working fluid circuit, comprising a first heat exchanger connected in an exhaust gas line of and internal combustion engine and a second heat exchanger inserted into a line, which are part of the working fluid circuit, which has at least an expansion machine, a condenser and a fluid pump.

Such a waste heat recovery system is known from the German patent application DE 10 2013 211 875 A1. This waste heat recovery system has a working fluid circuit having two heat exchangers, wherein a first heat exchanger is connected in an exhaust gas line of the internal combustion engine and a second heat exchanger in an exhaust gas recirculation line of the internal combustion engine. The working fluid circuit furthermore comprises an expansion machine, a condenser and a fluid pump, wherein the working fluid circuit is divided into two fluid branches downstream of the fluid pump, which lead respectively to the first heat exchanger and the second heat exchanger. A distributor valve is initially inserted into the fluid branches, which adjusts the amount of the working fluid supplied to the heat exchangers.

A two-stroke vane cell pump is known from the furthermore known German patent application DE 10 2014 212 920 A1, which, for example, is used as a pre-feed pump of a fuel injection systems of an internal combustion engine. The vane cell pump has a stator with a rotatably arranged rotor therein.

SUMMARY OF THE INVENTION

The aim underlying the invention is to provide a waste heat recovery system that is improved in particular in respect of an efficiency of the system.

This aim is met in that each of the two heat exchangers is assigned a fluid pump. In so doing, the working fluid circuit is divided into two working fluid branches on the output side of the two fluid pumps, wherein the first heat exchanger is connected into the first working fluid branch and the second heat exchanger into the second working fluid branch. The working fluid branches are again joined to the working fluid circuit on the output side of the two heat exchangers. By means of this configuration, valves present in a conventional waste heat recovery system, which adjust a quantity distribution of the working fluid to be fed back to the two heat exchangers, can be omitted. As a result, a drop in pressure in the working fluid, which accompanies a valve and is energetically undesirable, can be prevented. Thus, an improvement in the waste heat recovery system in particular with regard to the efficiency thereof is achieved. In addition, valves are subject to tolerances with regard to the adjustment thereof. By eliminating the valves, these adjustment tolerances are likewise omitted.

In a modification to the invention, the fluid pumps are combined in a double pump. Although the two fluid pumps can basically be designed as single pumps, the preferred embodiment in the form of a double pump is depicted. Such a double pump only requires a drive and a pump housing so that the construction costs are only slightly raised—if at all—with respect to a single pump.

In a further embodiment of the invention, the double pump is designed as a two-stroke vane cell pump. A two-stroke vane cell pump is, for example, basically known as a hydraulic pump for a fuel injection system or also for a transmission. In this regard, the construction costs for such a two-stroke vane cell pump are only negligibly higher with respect to a single-stroke vane cell pump, so that the costs for such a two-stroke vane cell pump are actually the same in comparison to a single-stroke vane cell pump if the cost savings on the valves are considered. As the case may be, a cost advantage is even achieved.

In a further embodiment of the invention, respectively one first displacement chamber of the two-stroke vane cell pump is connected to the first heat exchanger via a first supply line and a second displacement chamber of the vane cell pump to the second heat exchanger via a second supply line. The two supply lines form the aforementioned working fluid branches. The construction costs for implementing an inventive waste heat recovery system of this type are low by means of this embodiment.

In a further embodiment of the invention, the vane cell pump can be operated with respect to a delivery quantity distribution into the first displacement chamber and into the second displacement chamber at a constant or adjustable total delivery quantity. In so doing, a delivery quantity distribution into the first displacement chamber and the second displacement chamber occurs between 0 and 100% and vice versa between 100% and 0% or respectively vice versa. The total delivery quantity can be specified by a rotational speed setting, for example by means of an electric drive. The variable delivery quantity distribution can therefore be described without a significant loss. This too leads to an increase in the efficiency of the system.

In a modification to the invention, the two-stroke vane cell pump has a stator that is radially displaceable with respect to a motor. The vane cell pump designed in this manner can easily be adjusted with respect to the desired delivery quantity distribution.

In a further modification, provision is made for a spindle adjustment using a spindle for displacing the stator. This represents the preferred embodiment for adjusting the stator, wherein other adjustment devices are, however, also conceivable.

In a modification to the invention, a step motor for actuating the spindle is provided. Such a step motor is characterized by a high degree of adjustment accuracy while having a robust construction and low drive capacity. Within the scope of the invention, other adjustment devices are, of course, conceivable for actuating the spindle or directly for adjusting the stator.

In a modification to the invention, the line comprising the second heat exchanger is an exhaust gas recirculation line of the internal combustion engine. Even if the second heat exchanger can be arranged in any line of the internal combustion engine for conducting heat energy, the preferred use is in fact given by an exhaust gas recirculation line.

Further advantageous embodiments of the invention can be extracted from the description of the drawings, in which an exemplary embodiment of the invention depicted in the drawings is described in detail.

BRIEF DESCRIPTION OF THE DRAWINGS

Further measures for improving the invention are depicted/described below in detail using the figures together with the description of the preferred exemplary embodiments of the invention.

In the drawings:

FIG. 1 shows a schematic diagram of a waste heat recovery system configured according to the invention and comprising a working fluid circuit, and

FIG. 2 shows a schematic cross-sectional view of a two-stroke vane cell pump, which is used in a working fluid circuit according to FIG. 1.

DETAILED DESCRIPTION

The waste heat recovery system schematically depicted in FIG. 1 has a working fluid circuit 1 comprising a first heat exchanger 2 a and a second heat exchanger 2 b. The heat exchangers 2 a, 2 b are designed here as evaporators or respectively function as such and are adapted to an internal combustion engine 5 for the recovery of waste heat generated during operation of the internal combustion engine 5. An exhaust gas stream 4 of the internal combustion engine 5, which is conveyed in an exhaust gas line 3 of the internal combustion engine and forms a waste heat flow, flows through the first heat exchanger 2 a. In addition to the first heat exchanger 2 a, the second heat exchanger 2 b is inserted in a line in the form of an exhaust gas recirculation line 6 or in another heat carrying line. Via the exhaust gas recirculation line 6, a partial quantity of exhaust gas is extracted from the exhaust gas stream 4 and supplied in a controlled manner to an air intake system 8 of the internal combustion engine 5 via an exhaust gas recirculation line valve 7. The air intake system 8 can also be designed here as a charging air line system. The two heat exchangers 2 a, 2 b can, if applicable, be bypassed via heat carrying bypass lines, which are not depicted, at certain operating states of the internal combustion engine 5 of a vehicle in which the internal combustion engine is installed.

During operation, fuel and combustion air are supplied to the internal combustion engine 5, which combust in combustion chambers of the internal combustion engine 5 to hot exhaust gas while generating output, said exhaust gas forming the exhaust gas stream 4 during operation of the internal combustion engine 5. In the process, the exhaust gas stream 4 is finally discharged through the exhaust gas line 3, from which the exhaust gas recirculation line 6 also branches off, into the surrounding environment. Exhaust gas mufflers 9 as well as devices 10 for the after-treatment of the exhaust gas in the form of, for example, a catalytic converter and/or a filter can be installed in the exhaust gas line 3 upstream and/or downstream of the first heat exchanger 2 a. The internal combustion engine 5 is, for example, a self-igniting internal combustion engine which is operated with diesel fuel. Thus, the diesel fuel is injected, for example, by means of a common rail injection system into the combustion chambers. The internal combustion engine can, however, also be an internal combustion engine that is externally ignited and operated with gasoline and can likewise have a common rail injection system.

The first heat exchanger 2 a and the second heat exchanger 2 b are, as previously embodied, in turn part of the working fluid circuit 1, which, besides the heater exchangers 2 a, 2 b, comprises an expansion machine 11, a condenser 12, if applicable a condensate pump, an expansion tank 14 and two fluid pumps 15 a, 15 b. The fluid pump 15 a is fluidly connected to the first heat exchanger 2 a via a first supply line 25 a and the second fluid pump 15 b is fluidly connected to the second heat exchanger 2 b via a second supply line 25 b. The fluid pumps 15 a, 15 b are illustrated as autonomous pumps in the depiction according to FIG. 1 for reasons of clarity, actually, however, preferably combined in a two-stroke vane cell pump 16 (see FIG. 2). This two-stroke vane cell pump 16 can be adjusted such that, in the case of a constant or preferably adjustable total delivery quantity, a delivery quantity distribution to the first heat exchanger 2 a and the second heat exchanger 2 b can be adjusted so as to increase and correspondingly so as to decrease between 0% and 100%. The total delivery quantity can, for example, be adjusted by means of a change in the rotational speed of the electrically driven vane cell pump 16.

The expansion machine 11 can, for example, be a piston machine or a turbine. In the case of a turbine, a reduction gear is arranged downstream in order to reduce the high turbine rotational speeds and to adapt these speeds to the rotational speeds of a working machine connected downstream or to another consumer.

During operation of the waste heat recovery system, a fluid suitable for a Rankine cycle is brought to a high pressure by the two-stroke vane cell pump 16 and supplied to the heat exchangers 2 a, 2 b. The fluid is heated in the heat exchangers 2 a, 2 b and transferred under a high pressure into the vaporous state. The steam generated in this manner is supplied to the expansion machine 11 and drives the same while expanding the working fluid. In order to be able to lead the working fluid circuit 8 past the expansion machine 11, a bypass line 17 comprising a bypass valve 18 can be provided, via which the expansion machine 11 can be bypassed.

The working fluid supplied to the expansion machine 11 is expanded in said machine under provision of mechanical shaft work, which is discharged via an output shaft 19. After that, the “cold” steam is condensed in the condenser 12 and finally supplied again to the two-stroke vane cell pump 16. The expansion tank 14 is connected into the connecting line between the condenser 12 and the two-stroke vane cell pump 16. In addition to the previously described components, any other further components, in particular sensors for ascertaining temperatures and pressures in different sections of the working fluid circuit, can be present.

FIG. 2 shows a schematic cross-sectional depiction of the two-stroke vane cell pump 16. The two-stroke vane cell pump 16 has a stator 20, which is arranged in an axially displaceable manner in a housing of the two-stroke vane cell pump 16, which housing is not depicted. This will be further described below. A rotor 21 is arranged in a rotatable manner within the stator 20, wherein the rotor has a number of slots in which vanes 22 are arranged in a longitudinally displaceable manner. Under inclusion of the stator 20 and the rotor 21, a first suction region 23 a and a first displacement chamber 24 a as well as a second suction region 23 b and a second displacement chamber 24 b (that are in each case depicted by a curved arrow) are formed in the housing of the two-stroke vane cell pump 16. The first suction region 23 a and the second suction region 23 b are connected to one another within or outside of the pump housing and are connected to the working fluid circuit 1 at the output side of the condenser 12 or respectively the condenser pump 13. The first displacement chamber 24 a is connected to the first heat exchanger 2 a via the first supply line 25 a that forms a working fluid branch; and the second displacement chamber 24 b is connected to the second heat exchanger 2 b via the second supply line 25 b.

The stator 20 is, for example, connected to a spindle 26, which in turn is connected to a step motor 27. By means of the step motor 27, the spindle 26 can be adjusted in accordance with the double arrow above the stator 20. Thus, the stator 20 is adjusted radially with respect to the rotor 21 and therefore the first suction region 23 a and the first displacement chamber 24 a are enlarged and at the same time the second such region 23 b and the second displacement chamber 24 b are reduced in size or respectively vice versa. As a result, a continuous adjustment of the delivery quantity distribution is adjusted into the first supply line 25 a and the second supply line 25 b. The working fluid circuit 1 configured in this way gets by without conventionally installed valves in the first supply line 25 a and the second supply line 25 b. In this way, an increase in efficiency of the waste heat recovery system is achieved. 

1. A heat recovery system having a working fluid circuit (1), the heat recovery system comprising a first heat exchanger (2 a) connected in an exhaust gas line (3) of an internal combustion engine (5) and a second heat exchanger (2 b) inserted into a line, wherein the first and second heat exchangers (2 a, 2 b) are part of the working fluid circuit (1), wherein the working fluid circuit also has at least an expansion machine (11), a condenser (12) and first and second fluid pumps (15 a, 15 b), and wherein the first and second heat exchangers (2 a, 2 b) are respectively connected to the first and second fluid pumps (15 a, 15 b).
 2. The heat recovery system according to claim 1, characterized in that the first and second fluid pumps (15 a; 15 b) are combined in a double pump.
 3. The heat recovery system according to claim 2, characterized in that the double pump is a two-stroke vane cell pump (16).
 4. The heat recovery system according to claim 3, characterized in that a first displacement chamber (24 a) of the vane cell pump (16) is connected to the first heat exchanger (2 a) via a first supply line (25 a) and a second displacement chamber (24 b) of the vane cell pump (16) is connected to the second heat exchanger (2 b) via a second supply line (25 b).
 5. The heat recovery system according to claim 3, characterized in that the vane cell pump (16) is configured to be operated with respect to a delivery quantity distribution into the first displacement chamber (24 a) and into the second displacement chamber (24 b) at a constant or adjustable total delivery quantity.
 6. The heat recovery system according to claim 5, characterized in that the vane cell pump (16) has a stator (20) configured to be radially displaced in relation to a rotor (21).
 7. The heat recovery system according to claim 6, characterized in that the vane cell pump has a spindle adjustment using a spindle (26) for displacing the stator (20).
 8. The heat recovery system according to claim 7, characterized in that the vane cell pump has a step motor (27) for actuating the spindle (26).
 9. The heat recovery system according to claim 1, characterized in that the line into which the second heat exchanger (2 b) is inserted is an exhaust gas recirculation line (6) of the internal combustion engine (5). 